Maximizing Manure Storage Capacity


(Photo: A creative gutter system installed at Knoxland Farms in Bradford, Vermont. Engineers from the Agency of Agriculture can help design gutters that can withstand Vermont winters. )

By Clark Parmelee, VAAFM

The summer of 2017 has proven to be a very wet year. The amount of rainfall has made it challenging for farmers to get field chores done. When fields are saturated, crops can’t be planted or harvested, and manure cannot be applied. Between not having dry enough field conditions to spread manure and an above average amount of rainfall, several farmers have found themselves in the stressful situation of pushing the limits on the storage capacity of their manure pits. Even if there is nothing that can be done to change the weather, there are ways to make the most of on farm liquid manure storage.

When managing a manure pit, it is important to consider the amount of rainwater entering the pit. Every time a 1-inch rain event occurs, an acre of land will receive 27,154 gallons of water. For every 1-inch of snow we receive, an acre of land will receive 2,715 gallons of water. In an average year Vermont receives about 37 inches of precipitation, this means about 1 million gallons of water falls on an acre of land annually.

If a farm has a manure pit with a half-acre of surface area and a quarter acre of other impervious surfaces draining to the pit, the farm will have about 400,000 gallons of rainwater to spread. This figure takes evaporation into consideration. Evaporation rates tend to be higher in the summer than in the winter though, meaning that a pit will typically contain more water in the spring than in the summer.  If a farm is operating a manure pit with a half-acre of surface area and they spread using tanks with a capacity of 4,000 gallons, the farm will haul roughly 100 loads of rainwater on an average year!

It is important to stop any additional clean water from entering the pit. Spreading costs can be lowered for farms if additional water from barn roofs is prevented from entering the pit. It is also important to make sure excess water isn’t entering the pit from the barn, whether it is rainwater entering the barn and then the pit, or plate cooler water going down the drain. Through the State’s Best Management Practices (BMP) Program, financial assistance is available to help pay for clean water diversion projects to reduce the amount of water entering manure pits.  

Another way to maximize the storage capacity of a manure pit is to consider if some of the manure produced on the farm is capable of being field stacked. Some farms use a dry manure system for groups such as heifers and dry cows, and liquid storage for their milking herd. Any manure that is at least 20% dry matter and is capable of being stacked 4 feet high, can be field stacked. The BMP Program can help farms find appropriate places to field stack, and help pay to install access roads to approved sites.

Hopefully the 2018 growing season will be drier than 2017, but it’s hard to say at this point. Though the weather cannot be controlled, it is important that farmers consider all their options in how manure is managed on their farm to prevent manure pits from overtopping.